1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light [herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays and gamma rays].
2. Description of the Prior Arts
Photoconductive materials, which constitute photoconductive layers in solid state image pick-up devices, image forming members for electrophotography in the field of image formation, or manuscript reading devices, are required to have a high sensitivity, a high SN ratio [Photocurrent (I.sub.p)/Dark current (I.sub.d)], spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during use. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon [hereinafter referred to as a-Si] has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German Laid-Open Patent Publication No. 2933411 an application of a-Si for use in an electro-photoconverting reading device.
However, under the present situation, the conventional photoconductive members having photoconductive layers constituted of a-Si are further required to be improved in a balance of overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics during use such as humidity resistance, and further stability with lapse of time.
For instance, when applied in an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are scheduled to be effected at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated use or so called ghost phenomenon wherein residual images are formed.
As another disadvantage, for example, according to the experience by the present inventors from a number of experiments, a-Si material constituting the photoconductive layer of an image forming member for electrophotography, while it has a number of advantages as compared with inorganic photoconductive materials such as Se, CdS, ZnO or organic photoconductive materials such as PVCz or TNF of piror art, is also found to have several probelms to be solved. Namely, when charging treatment for formation of electrostatic images is applied on the photoconductive layer of an image forming member for electrophotography with the photoconductive member being constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of prior art, dark decay is markedly rapid, whereby it is difficult to apply a usual electrophotographic method. This tendency is further pronounced under a humid atmosphere to such an extent in some cases that no charge is retained at all until development.
Further, when the photoconductive layer is constituted of a-Si materials, the photoconductive layer may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, and boron atoms, phosphorus atoms, etc. for controlling the electroconduction type as well as other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical, optical or photoconductive characteristics of the layer formed.
That is, for example, not scarcely the life of the photocarriers generated by light irradiation in the photoconductive layer formed is insufficient, or at the dark portion, the charges injected from the support side cannot sufficiently be impeded.
Thus, it is required in designing of a photoconductive member to make efforts to obtain desirable electrical, optical and photoconductive characteristics as mentioned above along with the improvement of a-Si materials per se.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid state image pick-up devices, reading devices, etc. Now, a photoconductive member having a photoconductive layer which comprises a-Si, particularly an amorphous material containing at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon atoms [hereinafter referred to comprehensively as a-Si(H,X)], so called hydrogenated amorphous silicon, halogenated amorphous silicon or halogen-containing hydrogenated amorphous silicon, said photoconductive member being prepared by designing so as to have a specific structure, is found to exhibit not only practically extremely excellent characteristics but also surpass the photoconductive members of the prior art in substantially all respects, especially markedly excellent characteristics as a photoconductive member for electrophotography. The present invention is based on such finding.